Near-infrared absorption of fused core-modified expanded porphyrins for dye-sensitized solar cells.

This article focuses on the theoretical investigation of fused core-modified expanded porphyrins containing two pyrrole rings, one dithienothiophene (DTT) unit, and varying numbers (1–4) of thiophene rings as potential dyes for dye-sensitized solar cells (DSSCs). Using density functional theory (DFT), time-dependent DFT (TD-DFT), and nonequilibrium Green's function methods, the study analyzes their photophysical, photovoltaic, and charge transport properties. The compounds exhibit strong absorption in the near-infrared (700–970 nm) and visible (500–645 nm) regions, with increased thiophene rings causing bathochromic shifts favorable for solar energy harvesting. All dyes show thermodynamically favorable electron injection into TiO2, but dye regeneration with the common I−/I3− electrolyte is only feasible for the smaller pentaphyrin and hexaphyrin derivatives. Charge transport simulations reveal that pentaphyrin and octaphyrin-based molecular junctions have significantly higher conductance at low bias voltages compared to hexaphyrin and heptaphyrin, with octaphyrin showing enhanced current at higher voltages. These findings suggest that expanded porphyrins, especially pentaphyrin and hexaphyrin, are promising candidates for DSSC applications due to their favorable absorption and electronic properties.